Process of treating carbon brushes



Patented `une 22, 19423 UNITED -rRo'oEss "or TREATING cAR-BoNBRUsHEs tion of Pennsylvania Nomawing. Application october 1a i944.

Serial No. 558,466

This invention relates-to the treatment 'o'f carbon brushes and more `parti'cu'larly toa process iorapplyi-ng `to carbon brushes predetermined amounts of lead halide compounds capable 'of improving the operating characteristics thereof.

It iskncwn that copper commutators and Isli'p rings, when` operating against carboni brushes under ordinary atmospheric conditions,4 `dei'elop a nlm cnv the surface of the commutator or "slip ring which imparts good operating characteristics to the combination. A `.particular feature of this -ilm isa low coefficient of friction'. With a properly built-up Jvfilm on\ thev surface of-'the .conmutator or slip ringthe carbonbrushwill operate for `pr i longed periods of time with a` relatively insignificant rate of Wear. r

On the other hand, under certain adverse-conditions which may be met at high alttude'afr example, the iilm on copper commutatrs istiecomposed or broken down and' will not lbe built up. Carbon brushes operating againstth Leommutator lacking the desired film will 'Wear dust at an exceedingly rapidrate. n aircraft motors and generators, carbonbrushes have been known to dust at rates of. T16." anfhour and'i'nre at altitudes lof 40,000 feet. Likewisei l `'Ceiifafl'r transportation service, suchas on railway and Streetcar service, the benecial ln'i von copper commutators in the motors thereofmay'vct be present, or only partially preset A Carbon brushes in such equipment havebeen .known to Wear at an excessive rate,`th"ereby requiringfrequent lay-oversoi locomotives for replacement of the carbonibrushes., In some` cases,. the ix'iehl-V cient oi friction of the commutatorsof =electrical railway locomotives has been so high that-'the carbon brushes have been brokemthereby causing Unsatisfactory service ofkthe equipment.

It has been discovered thai-)certain halide compounds of metals,` whenV applied to, .or incorporated Within, `carbon brushesgpromote the building up of a benecial onthesurface of the commutatore even under the most adverse conditions, thereby -greatlyreducing 4the rate of Wear and dusting` of the=brushesj Howeverjnot all metal. halidesare satisfactory for this-purpose. Hydroscopic or deliduesoent metal halides in particular have been foundtobe undesirabley since they will absorb sufficient moisture from the atmosphere for the metal `halide/to. 4dissolve inl the condensedv Water and l'fo-drair-iy out ofthe brushes; rIhe halides ofthe alkalimetals are not suitable in somecases, since` theyl ,appear `to decompose and .form the alkali hydroxides` and cause excessive sparking` and-` otherw-ise detrimentally affect the. operating. on 4thecarbon brusheseagainst comniu-tators.4 'y Therefore only a few metal-halides are reasonablyuseful for brush applications.` i y f AI possible explanationforA the eiectiveness of Minime. (ol. 117-121) the metal halides in producing satisfactory films on commutators is as follows'. The metal halide, for example,` lead chloride, Within 'the carbn brush at the point of contact With the copper commutator is heated andV by reason of the heat or in combination' with the effects of the passage .of electrical current decomposition vand 'reaction with the copper surface takes place to produce a copper chloride. However, the copper chloride so produced is unstable arid 'even in the' presence of small traces of oxygen readilyfreacts to`form 'a copper oxide film or coating. `Exterisive exper'm'entation indicates that the lm on copper oommutators is a copper oxide 'coating Which is duplicated bythe lm produced by the' interaction of the metal halide Witljij the copper. In 'any event, results in service indicate' that a beneiici'al film resulting in theoptimum' perform ance of carbon brushes and copper commutator results' when metal halides arev present in the brushes. In fact, in some cases commutators' which were in a rough and unsatisfactory condi'- tion on certain electric railvvay mo't'ors u'sin'g un'' treated carbon brushes Were greatly improved after several thousand" hours" operation against carbon brushes carrying metal halides.4

n In `order to provide for the retention for the life of the brush of the metal halide applied `thereto in predetermined amounts, it is preferred to' use metal halides having a high` melting;l temperature and a highV boiling temperature, thereby assuringr an: exceedingly lotvvapo'r pressure'uhd'er the conditions of operation. Brush and com# mutancr temperatures gf fiomioo c; to 2005. are not uncommon. Metal halideshavig a low boiling point by comparison will steadily eva'p'f rate when" the'brush to which they `are applied becomes heated' during use. Therefore, the latr ter metal halides will be present in smaller amounts 'with passage of `time and eventually little or no metal halide Will be present.` u

The process of applying toA or incorporatin in brushes the metal halid'esi'srenderetl" quitedifficult whenv metal halide's are' selected .that meet' the'dsirable requirementsherein listed. A hi'gh mening point metal halide is difficult to melt and applyin molten state to the 'c'arbon`bru`sh. Prolonged imrhrsinhas been found only moderately satisfactory to cause the' metal halide to pene: trate" the' pores oiabrus'h. Due to the highn'ielt`I ii'g temperatures, problems of decompositionand diflicultyy iri handling liquidsl heated to highteni peratures enter the picture. A decided health hazard is encountered, since the lead vapors from molten haldes are present and are' quite dangerous. Solutions ofmetaIhalides sufficiently cocentrated to permit a practical amount of metal halide to be absorbed bythe porous brushes are notffeasible in most cases. For certainztiee conditions such as are encountered in aircraft operation to be satisfactory brushes must carry as muchas 50% by weight of metal halide. The problem of incorporating this amount of metal halide in a carbon brush therefore is considerable.

The object of this invention is to provide a process for impregnating carbon brushes with a' predetermined amount of a. metal halide.

A further object of the invention is to prepare y solutions of lead halides having a high concentration oi the halide therein to provide for economically impregnating carbon brushes with prenot 'be leached out in service where Water may be encountered in one Way or another. Carbon brushes impregnated With varying amounts of one or more of these lead halides have given excellent service in cooperation with copper commutators and slip rings in many varieties of extreme surface conditions.

It has been discovered that concentrated solutions of lead chloride, lead bromide or lead iodide or mixtures of any two or all three may be prepared by preparing an aqueous solution containing lead, ammonium, acetate and the respectivehalide radical. YThe maximum weight of lead halide which may be dissolved in the solutions is closely related to the weight of the ammonium acetate present in the solution. As the concentration of ammonium acetate in the ammonium solution is increased, an almost equivalent increase of the saturation point of the lead halide in the solution is attained. In addition, the maximum amount of the lead halide soluble in the solution increases somewhat with the temperature.

VA typical aqueous solution which has been prepared for the practice of the invention was composed of 40 parts by weight of lead chloride, 50 parts by weight of ammonium acetate and 50 parts by weight of water. In another case, a solution composed of '75 parts by weight of water and -parts by weight of ammonium acetate would only dissolve 20 parts by weight of lead chloride. In another case,'a solution composed of '70 parts by Weight of water and 70 parts by weight of ammonium acetate dissolved 40 parts by weight of lead chloride and 4 parts by weight of lead bromide. All of these solutions were used successfully in impregnating electrographitic brushes.

The lead halide need not be used assuch in preparing solutions of this invention. A mixture was prepared by combining:

, Water parts by weight 48.5

Lead acetate parts-- 41.25 Ammonium bromide do 21.4 Ammonium acetate parts by weight" 37.5

This solution was equivalent to one produced by dissolving 40 parts by weight of lead bromide in a solution composed of 50 parts by weight of water and 50 parts by weight of ammonium acetate. Solutions have been prepared by mixing predetermined proportions of lead acetate, ammonium chloride, ammonium acetate and water. Mixtures of ammonium chloride and ammonium bromide and ammonium iodide orany two may be prepared as decided.

The relatively concentrated lead halide solutions prepared by any of the processes herein set forth may be applied to either carbon plates after graphitizing treatment or to brushes that have been fully machined and cut to shape. The brushes or carbon plates are disposed in the concentrated solutions of the lead halide for a few minutesin order to soak up the solution in the pores of the carbon body. Preferably the brushes are subjected to vacuum before the solution of lead halide is applied thereto in order to expedite the impregnation. Electrographitized carbon has a greater porosity than metal graphite brushes, which are not subjected to the high temperature baking treatment of the former. The extensive porosity of the graphitized brushes renders them more amenable to the practice of the present invention.

After the carbon bodies have absorbed suncient of the solution, generally a volume of solution equivalent to about 25% of the volume of the brush will be absorbed by a graphitized plate or lbrush, the carbon bodies may be removed from the solution. The brushes soaked with the solution are then subjected to a heat-treatment rst to drive off the water and then the temperature is increased to cause the ammonium acetate to decompose into volatile components. It is believed that the ammonium acetate will decompose into water and acetamide. Five hours heat-treatment at 180 C. has been found suicient to remove all but the lead'halide. The lead halide component of the solution is disposed 4throughout the pores of the carbon brush member. If the amount of lead halide present is insu'cient for the intended use of the brush, one or two additional treatments may be necessary. For brushes to be employed in extreme aircraft applications, three impregnations employing a concentrated lead chloride solution containing 40 grams of lead chloride per 100 cc.rof a solution composed of equal parts by weight of ammonium acetate and water will apply to the brush about 20% of its weight of lead chloride. For railway locomotive service, a single application of a similar solution or even a much less concentrated solution is usually entirely adequate. The amount to be applied to the brush depends upon the requirements of the service to which the brushes are to be put.

The electrical properties of carbon brushes incorporating lead chloride, lead iodide or lead bromide are not adversely adected. When applied to electrical generators, the brushes have given excellent electrical service with a long life. Brushes treated -according to the invention have met all the requirements imposed thereon and have been found to be fully dependable. The performance of many types of apparatus embodying such brushes has been improved and the necessity of replacing brushes at predetermined inter- ,i vals previously required in noncritical locations has been reduced. Therefore, the brushes meet commercial and industrial requirements.

The process set forth herein enables the brush manufacturer to economically and conveniently prepare brushes having desirable wear and non- Since certain changes in carrying out the process embodied in the invention described herein may be made Without departing from .its scope, it is intended that all matter contained in the above description shall be interpreted as illusrtrative and not in a limiting sense,

I claim as my invention:

1. In the process of treating a carbon Ibrush to apply -thereto a lead halide -compound to improve the operating characteristics thereof, the steps comprising producing an aqueous solution containing substantial amounts of ammonium acetate, dissolving a lead compound selected `from the group consisting of lead chloride, lead iodide and lead bromide therein, applying the solution to the carbon brush, and heat treating the brush first to evaporate the moisture, thereby precipitating within the pores of the brush the lead compound and ammonium acetate, and then to decompose the ammonium acetate into subl chloride, iodide and bromide, to provide a solution having dissolved therein a large amount of the substances containing the radicals, applying the aqueous solution to the carbon brush and heat-treating the carbon brush to a temperature sui-cient lto evaporate the water and the ammonium and acetate radicals therefrom thereby precipitating the lead halide compound in the pores of the carbon brush.

3. In the process of treating a carbon brush to apply thereto a lead halide compound to improve the operating characteristics thereof, the steps comprising producing an aqueous solution containing of the order of from to 50% by Weight of ammonium a-cetate, dissolving to about saturation of a lead compound selected from the group consisting of lead chloride, lead iodi-de and lead bromide therein, applying -the solution to the carbon brush, and heat-treating the brush Iirst to evaporate the moisture, thereby precipitating within the pores of the brush the lead 6 compound and ammonium acetate, and then to decompose the ammonium acetate into substances that volatilize leaving only the lead compound in the pores of the carbon brush.

4. In the process of treating a carbon brush to apply thereto a lead halide compound to improve the operating characteristics thereof, the steps comprising producing an aqueous solution containing substantial amounts of ammonium acetate, dissolving a lead compound selected from the group consisting of lead chloride, lead iodide and lead bromide therein, applying the solution to the carbon brush, heat-treating the brush rst to evaporate the moisture, thereby precipitating Within the pores of the brush the lead compound and ammonium acetate, and then to decompose the ammonium acetate into substances that volatilize leaving only the lead compound in the pores of the carbon brush, reapplying the solution to the carbon Ibrush and heat treating to deposit more lead compound in the carbon brush.

5. In the process of treating a carbon brush to apply thereto a lead halide compoundto improve the operating characteristics thereof, the steps comprising, dissolving `in water substantial amounts oi substances containing only ammonium, a-cetate and lead radicals and a halide radical selected from the group consisting of chloride, iodide and bromide, to provide a solution containing more radicals Ithan the Water by Weight, applying the aqueous solution to the carbon brush, heat-treating the carbon brush to a temperature suicient to evaporate the Water and the ammonium and acetate radicals therefrom thereby precipitating the lead halide compound in the pores or" the carbon brush, reapplying the solution to the carbon brush and heattreating to deposit more lead compound in the carbon brush.

LAWRENCE E. MOBERLY.

REFERENCES CITED UNITED STATES PATENTS Name Date Adolph Sept. 28, 1909 Number 

